Method of making plastic bridgework



NOV. 27, 1951 F E TH METHOD OF MAKING PLASTIC BRIDGEWORK Filed Aug. 22. 1949 FIG. /2

INVENTOR Patented Nov. 27, 1951 UNITED STATES PATENT- OFFICE METHOD OF MAKING PLASTIC BRIDGEWORK Frank J. Barth, Jamaica, N. Y., assignor or onehalf to Edward Fraundorfer, Rego Park, New

York

Application August 22, 1949, Serial No. 111,615

1 Claim. (Cl. 1855.1)

This invention is concerned with a type of dental bridgework whereon artificial plastic teeth ous and many. In bridgework of this construction there is considerable strength in the bond of the teeth with the metal bridge frame whereby the possibility of the teeth becoming loose or out of alignment is negligible. Because of the perfect alignment of the teeth on the framework there are no food retaining pockets or crevices nor, because of the integral nature and strength of the bond of the teeth to the framework, is there any chance of the teeth loosening to create such pockets. Heretofore, cement has been used in securing artificial teeth to the bridgework. The use of cement made it most difiicult to obtain a proper alignment of a tooth with the metal frame of the bridge. In time the cement gradually washed out causing loose teeth and creating foodretaining pockets.

' Bridgework with artificial plastic teeth molded directly. thereon as an integral partof the metal framework and in perfect alignment with such framework is obtainable through use of my constructive casting investment teeth. These investment teeth are fashioned of dental investment material, and are made in various sizes and shapes to permit making of all types of bridgework. The investment tooth serves as a guide in the casting of the metal frame of the bridge, and has a post hole for the casting of a threaded anchor post integral with the framework. The investment tooth further serves as a guide for the making of the finished plastic tooth and its accurate alignment on the metal frame of the bridge. The various steps involved in constructing the finished bridgework by means of this constructive casting investment tooth constitutes a decided improvement in the art.

Therefore, the general object f this invention is a dental bridgework wherein an artificial tooth of plastic is molded and formed in perfect alignment directly on the metal framework of a bridge, and is further secured thereon by means of a threaded anchor post integral with the framework.

Another object of this invention is a method of making such bridgework.

A more specific object of this invention is a constructive casting investment tooth that has a threaded ovoid post hole, and which tooth is useful in the making of bridgework.

Other advantages and other objects of this invention will appear as this specification unfolds in detail and as it is read in conjunction with the accompanying drawings, wherein a specific embodiment of the invention is illustrated.

In the drawings,

Fig. 1 represents a constructive casting tooth in perspective;

Fig. 2 is a bottom view of the constructive casting investment tooth;

Fig. 3 is a cross section of Fig. 1 taken on line Fig. 4 represents an investment tooth of the pontic type;

Fig. 5 represents an investment tooth of the facing type;

Fig. 6 is an ovoid threaded post of wax;

Fig. 7 is a side elevation view of a dentist's plaster mold impression of a lower portion of a patients mouth with inlays in position and showing a molar space;

Fig. 8 is a side elevation view' with the investment tooth in position in the plaster model;

Fig. 9 shows the plaster model as inFig. 8, but with an index in position;

Fig. 10 shows the investment tooth as recessed preparatory to the casting of the metal framework for such;

Fig. 11 shows the recessed tooth as waxed in;

Fig. 12 is a view of the cast metal framework inlaid in the plaster model with a wax tooth thereon and with the index in position;

Fig. 13 is a view in perspective of the cast metal framework;

Fig. 14 is a view in perspective of the finished bridgework containing an artificial tooth of plastic molded and anchored thereon; and

Fig. 15 is a view of an ovoid metal sleeve adapted to fit about the anchor post.

In the drawings there is shown in Fig. 1 a .constructive casting investment tooth embodying my invention. This tooth is so called because it is used in the casting of the metal frame of a bridge as well as in the making of an artificial tooth or plastic. fhe tooth l is made of conventional dental casting investment material permitting it to withstand the high temperatures necessary in the casting of the metal frame for plastic bridge work. Extending vertically upwards into the tooth from its base 2 is an ovoid post hole 3. Thispost hole is provided with in- -o.v Qid post hole 3 surface of the tooth is provided with cusps and.

sulci I. The form of tooth illustrated in Fig; 1'

as embodying my invention is characterized as: of:

the tube type. Inasmuch as there are several dis-- tinct types of teeth used in the making of bridge-e work, the investment toothmay take, several forms, all, however, serving the same purpose. Besides the tube type there are pontics 8 and facing teeth 9. made in the several types and in various sizes to enable the making of all types of bridgework.

It can be seen that suitable molds may he used for making my investment teeth in large quantities, and that where'a round post hole is to be made little difficulty will beexperienced: But where an ovoid" threaded post hole is desired, for

post of wax with suitable annular undercuts or threads asin Fig. 6. 'I' then place dental investment material in a mold and around the ovoid wax post In. Upon hardening of the investment thewax post is then boiled out, leaving a threaded in the formed investment The investment tooth ma be necessary to a proper position in the vacant space. Its sides I6 are made to contact the adjoining teeth; its base 2 is saddled as at H to rest upon and fit about the gum I8; its occlusal surface, where required, is grounded so that its cusps and sulci I are in alignment with cusps and. sulci of opposing upper teeth.

The tooth I is then given a bath in hot wax. This fills the post hole 3 with wax preventing foreign particles from accumulating therein. This wax treatment also hardens the exterior surface of the tooth preventing it from being worn down through constant handling. The resulting waxy surface also aids; permitting ready separation of the tooth from; an index l9 that is made later on in the process.

he-wax. treatedtooth I is next repositioned in the. plaster model I2. An index I9 by usual methods is made of the tooth I in position. 'The In the use of the facing and pontic teeth 8-, 9

post hole to the outside of the tooth:

. It can be seen that there are many advantages'in the-making of dental bridgework through the use of my investment teeth. The investment tooth permits casting ofan ovoid anchor post integral with the metal frame. The-investment material of which the teeth are made is not only inexpensive, birt such material may be easily ground permitting accuracy of alignment of the finished tooth on the bridge frame. The investment tooth permits the making, and molding without cement of a finished plastic tooth directly on the metal frame, of the bridge. The finished bridgeworkobtained through the use of such investnient; teeth represents in the accurate alignment and strength of its parts a decided advance in the art.

- Through'the use of my investment-teeth I have devised an improved method in the making of plastic bridgework, whereby a plastic tooth is molded in accurate alignment directly onto the metal framework of a bridge. and is anchored thereon by means of a threaded anchor post, ovoid in form and integral with the metal frame of-thebridge.

In thedrawing's, Fig. 7, there is showna den tists model I2- in plaster of the lower section of a patient's mouth with a molar space I 3. The construction of a single-toothed plastic bridgework by myfimproved method will now be described.

Inlays M are first made on the teeth I5 immediately adjoining each side of the molarspace. Aconstructive casting tooth of the tube type I is selected'of asize slightlylarger than the'space I3 to be filled; This tooth is ground down where index is taken of the crown 20 and the facing side 24 of the tooth} For obvious reasons. the. index I9 includes; part of the adjoining teeth. Iii with theinlays thereon. The. importance or the. index IQ lies,- among other uses, in its: use later on inthe formation: of a wax duplicatev of tooth I as. well: as a finished plastic tooth.. The index. after being made is removed from the: plaster model. and sayed for use later onin the forming of. the duplie cate wax tooth.

The, gingival end.2*2 of. the tooth I.,with the exception of the. buccal'or facing side 2|, is; next coated with wax. Thethickness of the. waxcoat ing accurately predetermines the, thicknessot: the metal framework that. will. be. cast. This: advantageof. the. investment tooth in serving as a meansof predetermining the guagev ofithe. metal framework representsa decided advance; in the Prior'to coating the gingivalendfl with. wax,

theis'ides, I16; andthe-saddle H. are sli h ly recessed as at 23.- The sides I6 are recessedirom. theevident or vertical facing. margin line; 24. rearwards and upwards. to. the bitingv edge. Here. the. index 19. aids; in accurately determining the evident. line for recessingl. Thesaddle; is. deepened slightly and the lingual. or'back. side of the. toothisltecessed; from. the: saddle, I5. up, to the. gingivalline 2:5; The.- post. holeand. recessed portions: of. the tooth; arethen waxed his The. investment. tooth aswaxed inE appears. as1in Eig. ll...

.The. investment. tooth. as waxed in. is. next in.- vested with dental casting; investment. material. By:- conventional methods in. the. casting. process the. wax. Z5 isboiled out and replaced. by. metal to form. the framework of thebridge. Because ofithe threaded anchor post.5 formed in; theacaste ing process, the investmenttoothl isdestroyed so as to=remove it from-the; castframework; The resulting cast framework as in Fig. 13'. has a.

threaded vertical ovoid anchor post E-integral The" next step is concerned with duplicating the destroyed investment tooth in wax, andsub sequently'reproducing and moldingthe-wax-tooth in plastic directly onto the metal framework 6'.

The investment tooth I, destroyed in the process of removing it from the metal casting, is next duplicated in wax directly on the metal framework 6, through use of the index [9 that had been previously made.

The metal casting 6 is positioned on the plaster model and the index I9 is placed in its original position on the model as in Fig. 12. Hot wax is then poured into the space between the index I9 and the metal casting 6 and about the anchor post 5. Upon cooling of the wax and removal of the index IS the resultant wax tooth 21 represents a duplicate of the original investment tooth I. Use of the index l9 in this step eliminates the heretofore difiicult task of building such a wax tooth by hand.

The next step in the process is concerned with duplicating the wax tooth 21 in plastic. The bridge, which includes the metal framework with the wax tooth thereon is next invested with dental investment material by conventional methods. By a known process the wax tooth is boiled out and reproduced in plastic. It is to be noted that such plastic tooth 28 is not reproduced independently of the metal framework, but rather is produced or duplicated directly on the framework and about the ovoid anchor post 5.

The plastic material used in forming the finished tooth is that conventionally used in dental practice, and is preferably acrylic plastic.

Upon removal of the investment material we have a completed bridgework as in Fig. 14. The

. completed bridgework 29 has a finished acrylic plastic tooth 28 molded to the framework in perfect alignment and anchored thereon by the threaded anchor post 5.

It is to be noted that in the making of such bridgework 29 a tube type investment tooth I was used. In those cases where a facing tooth 9 or a pontic tooth 8 is required in making the bridge the process is the same. However, in preparing the facing and the pontic investment teeth for the metal casting, the post hole 3 and the backing 30 of the facing tooth are waxed up, while in the case of the pontic tooth the post hole 3, the backing 3| and an occlusal surface are waxed up. The resultant metal castings of the pontic and facing investment teeth will he the duplicate of the waxed in sections.

Because of the plastic material of which the finished teeth are formed, and since such teeth ae molded and securely anchored onto the metal frame of the bridge, there is little chance of such teeth becoming loose. However, for various reasons a tooth may become damaged necessitating its replacement. In such case after the damaged tooth is removed, a smooth sleeve of metal 32 is placed over the anchor post to block out the threads. An impression is taken in conventional manner. A finished acrylic tooth formed from the impression is cemented onto the bridge without necessitating the removal of the bridge frame from the patients mouth. It can be seen that not only does the post 5 serve to anchor at finished tooth to the framework, but it serves the added advantage of making such teeth interchangeable.

Having described my invention above, it is my intent, however, to claim such invention not only as described, but also in all such forms and varia tions as may reasonably be construed to be within the spirit of the invention and within the scope of the appended claim.

I claim:

A method of constructing plastic bridgework through use of an investment tooth having a threaded post hole. whereby such method a completed bridge is formed including the metal frame and a plastic tooth molded onto such frame and bound thereon by a threaded anchor post, and such method comprising positioning in a vacant dental space of a plaster model an investment tooth that has a threaded ovoid post hole, taking an index of the occlusal surface and evident facing sides of such tooth in position, recessing the saddle, the back of such tooth to the gingival line, and the sides from the saddle to the biting edge, waxing in the post hole and the recessed portions including the saddle, casting a metal frame of such waxed in sections, duplicating the original investment tooth onto such metal frame in wax, reproducing such wax tooth in plastic onto the metal framework.

FRANK J. BARTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 380,021 Carroll Mar. 27, 1888 1,037,489 Kelsey Sept. 3, 1912 1,826,271 Brooks Oct. 6, 1931 1,937,345 Jackman Nov. 28, 1933 2,357,757 Myerson Sept. 5, 1944 2,508,546 Skinner May 23, 1950 FOREIGN PATENTS Number Country Date 604,886 Germany Oct. 31, 1934 

